1. Field of the Invention
The present invention relates to a single lead adapted to be used with an implantable active device, such as a pacemaker, in dual pacing and/or sensing.
2. Description Of The Prior Art
Conventionally, dual chamber sensing/pacing has required one lead for the atrium and one lead for the ventricle, i.e. two leads have been implanted into the heart.
Different approaches has been made in order to make possible a good sensing signal from the atrium, which requires essentially a good contact between the sensing/pacing electrode and the inner wall of the atrial cavity. The atrial electrode has for instance been anchored in the atrium or be kept in close contact with the atrial wall mechanically by means applied on the outside of the body until the electrode has been fastened by ingrowth.
More recently, several approaches with single leads have been made.
In German Patentschrift 30 49 652, corresponding to PCT Application WO 80/02801 a bent lead is described which partly has the form of a spiral. The entire bent part has a form that is adapted to the inner cavity wall of the atrium. Apart from the bent part there is a second part which may have a dimension which is smaller than the dimension of the bent part. The shape of the bent part is such that a part thereof is kept in contact with the atrial wall. When the lead is in place it will be kept there until a layer of fibrin has covered the lead, which means that the lead actually will be fastened to the atrial wall.
Another solution is described in U.S. Pat. No. 4,154,247 in which the lead comprising a layer of a repeatable thermally-activated material, is heated before implantation and thereafter the lead is shaped into a non-linear configuration, reforming the lead into a linear configuration, inserting the lead to make electrical contact with the body organ and discontinuing the straightening of the pacer lead. Thus the lead is devised with more geometric variations at the atrial electrode. For example in one embodiment the electrode lead is laid in a circle to enable the atrial electrode to establish continuous contact with atrial tissue.
Yet another solution is described in the U.S. Pat. No. 5,476,499 where a single lead having an atrial electrode at a distal end for implantation in the atrium before the electrode lead is advanced deeper into the heart so a ventricular electrode in-line with and preceding the atrial electrode along the lead, is connectable in the ventricle of the heart. The ventricular electrode is affixed to the ventricular trabecular network. The part of the electrode distal to the ventricular electrode, i.e. the part between the ventricular electrode and the atrial electrode is made significantly thinner than the rest of the electrode lead. This lead has to pass through the tricuspid valve twice.
The greater part of the atrium inner wall from the vena cava superior and downwards does not exhibit any trabecular network which conventionally may be used for the fastening of the electrode or electrodes the wall is smooth.